Method and means for producing a long impulse for high energy rate forming apparatus



May 28, 1968 w. N. PRATT 3,335,375

METHOD AND MEANS FOR PRODUCING A LONG IMPULSE FOR HIGH ENERGY RATE FORMING APPARATUS Aug. 1. 1966 Filed United States Patent 3,385,375 METHOD AND MEANS FOR PRODUCING A LONG IMPULSE FOR HIGH ENERGY RATE FORMING APPARATUS Wilson N. Pratt, Anaheim, Calif., assignor to General Dynamics Corporation, Pomona, Califl, a corporation of Delaware Filed Aug. 1, 1966, Ser. No. 569,183 Claims. (Cl. 173-1) ABSTRACT OF THE DISCLOSURE Cir This invention relates to the forming of metal parts, particularly to the forming of parts utilizing metal powder, and more particularly to a method and means of providing a long impulse time for high energy rate forming apparatus utilizing metal powder.

High energy rate forming (H.E.R.F.) apparatus are known in the art. For example, apparatus such as that commercially known as Dynapak and manufactured by the assignee of this application and described, for example, in US. Patents 2,925,808; 3,036,538 and 3,093,117 illustrate H.E.R.F. apparatus which utilizes a high energy power source for driving the ram unit thereof at a high velocity rate. H.E.R.F. apparatus particularly adapted for forming three dimensional parts directly from metal powders has been developed and is described and claimed in copending application Ser. No. 427,665 and assigned to the same assignee of this invention. To illustrate the energy and velocity utilized by this type of apparatus, such as those illustrated and formed by the above referenced apparatus, utilizes approximately 14,300 foot pounds energy applied to a heated billet a velocity of 760 ft./sec.

Under certain conditions during the operation of the H.E.R.F. apparatus the ram bounces causing a second hit by the ram, which, in many caused breakage or deforming of the work accomplished. The energy causing the bounce is supplied by the ram and is energy which is wasted because it is not used to deform the billet to final o shape.

During the compaction of metal powder using a H.E.R.F. apparatus, it was determined that relatively thick sections of the finished part have a high density surface and a low density center. This effect is produced by a lateral release of pressure and a diminishing shock wave. It was determined that a longer impact time pulse would provide better transmission of the shock wave and result in a more uniformly dense part. Based on this concept, the present invention resulted which substantially stops the bounce of the H.E.R.F. apparatus ram; utilizes substantially all of the energy in the H.E.R.F. apparatus ram; and lengthens the pressure pulse of the ram.

Therefore, it is an object of this invention to provide a method and means for preventing undesirable bounce of the ram during operation of H.E.R.F. apparatus.

A further object of the invention is to provide an H.E.R.F. apparatus with method and means for effectively utilizing all of the energy in the ram thereof.

Another object of the invention is to provide a method 70 and means of lengthening the pressure pulse of H.E.R.F. apparatus.

ICC

Another object of the invention is to provide an improvement for H.E.R.F. apparatus which effectively accomplishes the forming of objects from metal powder by increasing the pressure pulse length thereof.

Other objects of the invention, not specifically set forth above will become readily apparent from the following description and accompanying drawings wherein:

FIGS. 14 are views partially in cross-section of a portion of a H.E.R.F. apparatus incorporating an embodiment for carrying out the invention and illustrating the action thereof during a forming operation;

FIGS. 5-7 illustrate various embodiments for carrying out the inventive concept; and

FIG. 8 illustrates another embodiment for carrying out the invention.

Broadly, the present invention relates to a ram construction for H.E.R.F. apparatus having means therein preventing substantial rebound or bounce of the ram and utilizing substantially all of the energy in the ram by lengthening the pressure pulse thereof. The means to accomplish these actions is in the form of a loosely confined mass within a chamber of the ram. The mass may be in the form of a liquid, powder, mixture, or magnetic material activated by a coil arrangement. The action of the mass may be modified by suitably designing the chamber within the ram so as to provide a relatively fast or relatively slow secondary pulse.

While devices having a loosely confined secondary mass within the mm or the like are known as illustrated by US. Patents 2,765,776, 2,899,936 and 3,022,838, none of these devices utilize a liquid, powder, etc. and the idea of utilizing various designs for a chamber within a ram for modifying the pressure pulse of the devices, as accomplished by this invention.

The forming sequence of a H.E.R.F. apparatus utilizing metal powders consists essentially of four operations; namely, heating the billet, transferring the heated billet to the die of the H.E.R.F. apparatus, forming the article by actuating (firing) the H.E.R.F. apparatus, and removing the formed article.

To accomplish the concept of this invention, the following procedure may be used:

(1) A hollow shaped chamber or cavity 10 may be machined into the ram 11 of the H.E.R.F. apparatus, ram 11 having a punch 12 attached thereto as shown in FIG. 1.

(2) The cavity 10 may be partially filled with a liquid, powder, or mixture of liquid and powder 13, for example, mercury and tungsten powder (see FIG. 1). If a mixture of liquid and powder is used, weight variations may be easily changed in the same cavity.

(3) When the H.E.R.F. ram [11 accelerates in the direction of the arrow, the inertia of the liquid-powder mixture 13 will cause it to collect in the end of the cavity 10 opposite to the direction of movement toward die 14 within which is positioned a billet or workpiece 15 of metal powder, as shown in FIG. 2.

(4) When the punch 12 on ram 11 contacts the work piece 15 and applies a pressure pulse, as indicated by the crooked arrow in FIG. 3, which generates a shock wave, the liquid-powder mass 13 will start to move forward in the cavity 10.

(5) The shock wave produced in the tooling (ram 11 and tool .12) without the invention moves to the rear surface and is reflected back. This wave unloads the tooling and produces bounce.

(6) If designed properly, the mass 13 in the cavity 10 will contact the forward face of the cavity (see FIG. 4) and produce pressures to overcome the eifect of tooling unloading and also produce a secondary shock wave. The secondary shock wave can be of relatively lower value to cancel out the reflected primary shock wave and the punch 12 will not bounce. If the cavity 10 configuration is properly designed the secondary pressure pulse may be extended over a relatively longer time. The longer time and the secondary shock wave will further compact (densify) the pulverent material 15.

FIGS. 5-7 illustrate different designs for modifying the secondary pressure pulse. FIG. 5 shows a ram 11' with a cavity therein designed for a relatively slow pressure pulse. FIG. 6 is designed for a very fast secondary pulse with short travel; while FIG. 7 illustrates a cavity 11' designed for a slower secondary pulse.

The genetic energy of the liquid-powder mixture may be calculated by the equation E=MV where: M =weight in pounds divided by 32.1 V=velocity of the ram This is why a heavy liquid-powder mixture is preferable. A mercury-tungsten mixture, for example, may be made twice as heavy as steel which means that the cavity within the ram can be relatively small. In compaction or forming of metal powder the faster the ram the shorter the secondary pressure pulse, thus the configuration of the ram cavity will be different when forming metal powder parts than when forming a solid billet.

Since mercury-tungsten mixture, for example, has a very high mass it provides better control of loss of energy due to lateral dispersion of the metal powder being formed. To control the lateral dispersion of the metal powder a longer pressure pulse at lower magnitude is required. With about a 3 to l compression ratio energy will start to be picked up from the liquid-powder mass before the punch stops and the result will be a long pressure pulse which inhibits rebound. The long continuous pulse is important in that it allows better control of H.E.R.F. apparatus energy and make this type of machine more competitive for forming metal powder parts.

FIG. 8 illustrates a method of controlling the fluidity of the liquid-powder mixture during the long impact pulse of the H.E.R.F. apparatus, wherein a powder of ferro magnetic material such as iron or iron aluminum alloy, etc. is added to the mixture. The mixture can then be stiffened by passing lines of magnetic flux through it. As shown in FIG. 8, the H.E.R.F. ram v11 is provided with a chamber of cavity 10" having a non-magnetic container 16 therein within which the magnetic liquid-powder mixture 13' is located. A coil 17 is positioned within the container 16 and is adapted to be connected to a power source as indicated by symbols. As in FIG. 1, punch 12 is operatively connected to ram 11".

In operation of the FIG. 8 embodiment, the coil 17 is energized before the first impulse occurs but after the ram 11" has started down and the semi-liquid (liquid-powder mixture) I13 is in the top of the chamber or cavity 10". When the magnetic flux lines pass through the ferro magnetic particles, it tends to hold the particles close to each other so that they do not want to move which restricts the flow of the mixture 13' which increases the apparent viscosity of the mixture. The force resisting deformation is thus magnetic and can be controlled by the amount of current through the coil 17, up to the point of saturation of the individual particles.

While a mercury-tungsten mixture further mixed with magnetic particles has been described above, other materials such as an oil and a ferro magnetic powder could be used. The concept behind the FIG. 8 embodiment is to stop splash and thus get more energy out of the liquidpowder mixture.

When the coil of FIG. 8 is energized magnetic flux flow tends to keep the small particles in contact with each other. This approach can be used to change a semi-fluid to a semi-solid which resists deformation. The lateral dispersion of the shock wave can thus be decreased in the semi-solid, which would then delivery more force over a longer time in the shaped chamber or cavity of the ram.

It has thus been shown that this invention provides a method and means for increasing the length of the pressure pulse in a high energy rate forming (H.E.R.F.) apparatus which additionally functions to substantially stop the bounce of the H.E.R.F. ram and utilizes all of the energy in the ram which results in a more uniformly dense part.

Although particular embodiments and materials have been illustrated and described for carrying out the invention, modifications will become apparent to those skilled in the art, and it is intended to cover in the appended claims all such modifications as come within the true spirit and scope of the invention.

What I claim is:

1. A method for increasing the impulse time of a high energy rate forming apparatus comprising the steps of: forming a cavity of desired configuration in the ram unit of the apparatus; providing the cavity with a desired amount of a suitable liquid-powder mixture which produces a secondary shock wave when the ram unit has been activated, and controlling fluidity of the' liquidpowder mixture by adding magnetic particles to the mixture and controllably passing lines of magnetic force through the mixture.

2, In a high energy rate forming apparatus adapted for forming articles from metal powder, the improvement comprising means for increasing the length of the impulse time and improving the density of the formed article; said means comprising a ram unit having a chamber therein, said chamber having a predetermined configuration, said chamber being partially filled 'with a suitable liquid-powder mixture, and means for controlling the fluidity of the liquid-powder mixture, whereby during actuation of the ram against an associated workpiece,

the liquid-powder mixture functions to produce a secondary pressure impulse which increases the length of the forming impulse and thus a more uniformly dense article to be produced.

3. The high energy rate forming apparatus defined in claim 2, wherein said last mentioned means includes means for passing magnetic lines of force through the mixture.

4. The high energy rate forming apparatus defined in claim 2, wherein said last mentioned means comprises a non-magnetic container positioned within said chamber, an electrical coil means operatively mounted in the wall portion of said container and adapted to be connected to an associated electrical power source, said liquid-powder mixture being retained within said container.

5. The high energy rate forming apparatus defined in claim 2, wherein said liquid-powder mixture is composed essentially of mercury and tungsten with ferro magnetic material mixed therein.

References Cited UNITED STATES PATENTS 1,678,957 7/1928 Philipp 92-176 X 1,876,917 9/1932 Gosslau 92176 X 2,153,501 4/1939 Harper 92176 X 2,635,490 4/1953 Kinker 173-127 X 2,899,936 8/1959 Edmund 92143 X 3,022,838 2/1962 Mitchell 173-102 X NILE C. BYERS, 111., Primary Examiner. 

